Generally speaking, in the context of differential gear mechanisms for a vehicle, either an inner race or an outer race of a bearing is fixed to the drive element, while the other race is positioned loose against an immovable element. It is thus possible to tilt the center of the bearing against the center of the drive element.
For this reason, the bearing is fixed onto the pinion shaft because the pinion shaft functions as a drive element which transmits the driving power of an engine, and the center of the pinion shaft and the center of the bearing are equal.
A conventional differential gear device is disclosed in Japanese Patent Application Laid-Open Publication No. 8(1996)-54096. In this differential gear device, a gear positioned between the pinion gear and the ring gear of the differential case must be adjusted when assembling the pinion mechanism and the differential carrier. This is because the gear position is closely related to the strength of the gear and the noise generated by the gear arrangement. This adjustment of the gear position is effected by changing the thickness of a shim that is arranged between the bolt and the pinion mechanism.
However, it has been found that this arrangement suffers from various disadvantages and drawbacks. In one respect, the outer race of the bearing that is arranged on the pinion mechanism may come into contact with the gear of the ring gear during pulling out of the pinion mechanism from the differential gear device. Therefore, the differential case has to be removed in an upward direction of the differential gear device, and then the pinion mechanism must be removed from the differential carrier. Further, the manner of adjustment of the gear position is not very desirable because it increases the assembly time.